Previous disaster studies could not adequately prepare the nation to address the mental health consequences of the September 11 terrorist attacks, although research including the Oklahoma City bombing study provided valuable information to guide early post-9/11 mental health interventions. New studies are needed to expand knowledge pertinent to such unprecedented large-scale terrorist incidents. Although new research has examined early mental health effects of the attacks on indirectly affected residents of New York City and the nation's population, in-depth psychiatric evaluation of the most highly exposed population--survivors from the upper floors of the World Trade Center (WTC) who escaped after the planes struck--has not been carried out. The combined expertise and resources of the highly experienced Washington University and University of Oklahoma Disaster Research Teams in collaboration with a New York City 9/11 research consortium proposes to apply state-of-the-art methodology to conduct indepth research on the mental health effects on this highly exposed population now accessible to this team through more than a year of networking. Focus groups currently being conducted with survivors are guiding the refinement of our assessment tools for the relevant and unique aspects of the 9111 experience. The proposed study will conduct diagnostic psychiatric assessments on 400 of the most heavily exposed survivors including workers of businesses on the highest floors of the WTC towers, and their spouses/ cohabitating partners (also obtaining secondary information on their children in preparation for our upcoming research with them). The study sample will be reassessed two years after the initial evaluation to examine longitudinal persistence of PTSD and other psychopathology. The aims of the study are to follow the course (from 2 through 6 years post-9/11) of posttraumatic stress disorder (PTSD) and other psychiatric disorders and ongoing treatment needs among this most highly exposed population, and to study their perceptions of justice and the burden of research participation on them. The findings will address important implications for conducting future research. They will inform the development and implementation of interventions aimed at restoration of individuals to fuller function in the post disaster workplace and at home with their families.